Shading

Better area lamp sampling using an area preserving parameterization paper This makes an area light sample a bit slower but it is usually more than compensated by the reduction in noise.(bc411ec06ef429)

A new "Max Bounces" option was added for lamps, which can be used to control how many light bounces the lamp will influence (fb820c063831)

Volume Rendering

Camera outside and inside a volume mesh

It is now possible to render with a camera that is inside of a volume mesh (fe731686fb31b6c)

Linear and cubic voxel interpolation

Support for cubic voxel interpolation This is helpful, especially for low-res smoke simulations, to avoid artifacts. The setting is per shader, and can be found below the volume sampling method menu, inside the Properties Editor. (d2d1b19170c579)

Optimization

Optimization for Mix RGB shaders (Mix blending mode), when the factor is 0.0 or 1.0 This reduces memory usage and improves performance a bit. (cbffc7499ef8)

Optimize math node without links to a single value node (6a4a911fc39ffc)